Impurities in Snow and its Radiative Forcing over the Arctic and Northern China

Summary

Light absorbing aerosols, like black carbon and dust particles, influence water, snowpack and the atmospheric energy budget in multiple ways. In addition to heating the atmosphere by absorbing solar radiation and interacting with clouds, light-absorbing aerosols deposited on snow reduce snow reflectance by darkening the surface, and accelerate snow melt. To explore the light-absorbing and snow-melting uncertainty in current Earth system models, a team of scientists led by a DOE researcher at Pacific Northwest National Laboratory compared the CAM5 simulations against the measurements collected from multiple field campaigns over the Arctic and Northern China. The team compared the energy forcing of black carbon associated with post-depositional enrichment that is partly determined by the snow-aging and melt-water scavenging treatment to the uncertainty resulting from the atmospheric deposition. They found that improving atmospheric black carbon deposition in CAM5 significantly reduces the bias of black carbon in snow over Northern China and the Arctic. Black carbon in snow is also sensitive to the two uncertain parameters that control the snow-aging and melt-water scavenging processes. First, the melt-water scavenging efficiency parameter plays a primary role in regulating black carbon concentrations in the Arctic through the post-depositional enrichment. Second, the snow-aging process shows more complex latitudinal and seasonal dependence. This study indicates that more in-situ snow impurity measurements are needed to better constrain uncertain parameters.